gistfile1.rb

MAIN FORM
<%= form_for(@project) do |f| %>
  <% if @project.errors.any? %>
    <div id="error_explanation">
      <h2><%= pluralize(@project.errors.count, "error") %> prohibited this project from being saved:</h2>

      <ul>
      <% @project.errors.full_messages.each do |msg| %>
        <li><%= msg %></li>
      <% end %>
      </ul>
    </div>
  <% end %>
  <div class="field">
    <%= f.label :diagram %>
    <%= f.file_field :diagram %>
  </div>
  <div class="field">
    <% if(@project.photo) %>
        <%= image_tag @project.photo %>
        <br />
    <% end %>
    <%= f.label :photo %>
    <%= f.file_field :photo %>
  </div>
  <div class="field">
    <%= f.fields_for :galleries do |builder| %>
      <%= builder %> 
      <%= render "gallery_fields", :f => builder %>
    <% end %>
    <p><%= link_to_add_fields "Add Image", f, :galleries %></p>
  </div>
  <div class="actions">
    <%= f.submit %>
  </div>
<% end %>

PARTIAL
<div class="field">
  <%#= link_to 'Destroy', project, confirm: 'Are you sure?', method: :delete %>
  <%= #nothing @gallery %>
  <%= #error gallery %>
  <%= #f %>
  <%= params %>
  <%= f.label :photo %>
  <%= f.file_field :photo %>
</div>